Perforated plates formed from ceramic fibers have been disclosed in numerous patents such as U.S. Pat. No. 3,954,387 to Cooper, U.S. Pat. No. 4,504,218 to Mihara et al and U.S. Pat. No. 4,673,349 to Abe et al.
A common use of perforated ceramic plates is as burner surfaces of gas burners. U.S. Pat. No. 5,595,816 of Carswell (the “'816 patent”), which is incorporated herein by reference, for example, discloses an all-ceramic perforated plate useful as a burner face. The plates of U.S. Pat. No. 5,595,816 are formed by pressurized filtration of a suspension of chopped ceramic fibers in an aqueous dispersion of colloidal alumina or colloidal silica through a mold having a perforated filter base and a pin support base having pins that extend through and beyond the perforations of the filter base. After formation, the perforated layer of chopped fibers is transferred to a dryer operating at a temperature not exceeding 650° F., for conversion into a strong perforated plate. As described by this patent an advantage of perforated ceramic plates for water heaters is maximized if they can function as flameless infrared burners emitting radiant energy directly to the bottoms of the upright water tanks.
U.S. Pat. No. 5,326,631 to Carswell (the “'631 patent”), which is incorporated herein by reference, describes a burner made with metal fibers, ceramic fibers and a binding agent. In this patent, metal and ceramic fibers are suspended in water containing both dissolved and suspended agents commonly used in the manufacture of porous ceramic fiber burners. These agents include a binding or cementing material such as a dispersion of colloidal alumina, and a pore-forming removable polymer such as fine particles of methyl methacrylate.
There is potential to improve on the characteristics of prior art burner surfaces in terms of the strength and durability characteristics, performance, BTU per hour per square foot firing rates, and manufacturing cost.